Many agrichemicals and pharmaceuticals are currently marketed as racemic or diastereomeric mixtures. In many cases, the desired physiological effect derives from only one enantiomer/diastereomer while the other enantiomer/diastereomer is inactive or even harmful or inhibitory. Chemical and enzymatic techniques for separating enantiomers are becoming increasingly important tools for production of chemicals of high enantiomer purity.
U.S. Pat. No. 4,898,822 describes the preparation of optically active indoline-2-carboxylic acids by hydrolysis of the corresponding racemic esters utilizing enzymes or microorganisms possessing stereoselective esterase activity. The substrates disclosed in that patent are compounds of the following general formula: ##STR1## wherein the chiral center indicated by the asterisk is a secondary-substituted .alpha.-carbon atom.
U.S. Pat. No. 5,202,260 and Yee et at., J. Org. Chem. (1992) 57: 3525-3527, disclose preparation of optically active acids and their corresponding esters by partial enzymatic hydrolysis of .alpha.-tertiary carboxylic acid esters using enzymes derived from Candida lipolytica. The enzyme utilized is derived exclusively from a single species of yeast, and solely transforms the S-ester of the racemic mix into its corresponding S-acid, leaving the R-ester intact.
Feichter et at., in J. Chem. Soc. Perkin Trans. (1991) 1: 653-654, disclose stereospecific hydrolysis of racemic methyl atrolactate via the action of, inter alia, .alpha.-chymotrypsin, resulting in formation of the corresponding R-acid and S-ester.
Peters et at., in Appl. Microbiol. Biotechnol. (1992) 38: 334-340, describe the stereospecific reduction of keto acids or esters to produce their corresponding chiral hydroxy acids or esters. Specifically, these authors demonstrate stereospecific keto ester reductase activity of Candida parapsilosis and Rhodococcus erythropolis wherein a racemic, acyclic, .beta.-keto acid ester is stereospecifically transformed into its corresponding chiral hydroxy acid ester.